Over the years, for the operations of stringing and maintenance of railway overhead lines, methods have been used that have depended upon existing technological solutions, which have been adopted for the construction of the operating machinery. However, these solutions meant that the above machinery could provide only limited operating performance.
The technological progress that has occurred over time has markedly improved the level of performance of the operating machinery, making available to the railway maintenance staff vehicles with increasingly high working performance: In particular, one of the major advances has regarded the units used for stringing overhead conductors.
Pullers or tensioners for stringing overhead conductors have evolved, from simple carriages equipped with a bullwheel for generating pulling or braking tension (whether single or in one or two pairs) and with other structures for guiding and supporting the conductors, into puller-tensioners. Puller-tensioners are operating machines that enable stringing of the conductors at the final operating tension, thus minimizing the manual effort required for geometrical positioning, both in a lateral direction and in height, through particular structures available to the operators (referred to as “masts”).
The devices currently used for laying the cable (conductor or support rope) are constituted by particular structures that enable manual positioning by sight on the part of the operator.
Their movement may moreover be limited by the presence of the conductors that have to remain in place in comparison to the ones that have to be replaced.
Some devices equipped with double bracket are moreover subject to the movement of the entire arm for correct positioning, thus causing imprecision due to the play and the masses of the structures involved.
The above devices are consequently subject to positioning errors (due to the intrinsic nature of the manual system), and there must consequently be envisaged adjustments, subsequent to laying and stringing of the conductors/support ropes, by further vehicles that follow the tensioning carriage with diagnostic pantograph or with counterweights of the infrastructure Consequently, the devices currently used present: uncertainty in positioning of the conductor/support rope; slowness of the operations of laying of the cable; problems of safety inherent in the operations performed manually; need for further specific vehicles for diagnostic operations on the cable installed.